Syrups and other sweeteners are used in the brewing, baking, soft drinks, canning and confectionery industries. Some of the more valuable syrups contain maltose; they are of industrial importance primarily because of their functional characteristics rather than their sweetness. Among the important functional characteristics of high maltose syrups are low hygroscopicity, low viscosity in solution, resistance to crystallization, low sweetness, reduced browning capacity, and good heat stability. Thus, maltose containing syrups can be used as moisture conditioners, crystallization inhibitors, stabilizers, carriers and bulking agents.
There are three important types of maltose containing syrups: (1) high maltose syrups; (2) extremely high maltose syrups; and, (3) high conversion syrups. The high maltose syrups have DE's (dextrose equivalents) of about 35-50, and a maltose content of 45-60%; the extreme high maltose syrups have a DE of about 45-60 and a maltose content of about 70-85%; and the high conversion syrups normally have a glucose content of 35-43%, a maltose content of about 30-47%. All of the foregoing syrups also contain some maltotriose.
The high conversion syrups are especially important because they have a high DE (e.g. 60-70) but they are stable enough to resist crystallization even at low temperatures down to 4.degree. C. and concentrations of up to 80-83% dry substance. Because of their high content of fermentable sugars (about 80% consisting mainly of maltose and glucose) these syrups are widely used in the brewing of beer, bread making and in the fermentation industries.
Highly purified maltose is also valuable and may be preferred to glucose in intravenous feeding at high concentrations because of its lower osmotic pressure and its slower release of glucose. As a result it also is more suitable for use in food for diabetics.
As the demand for starch derived syrups and sweeteners grows, it can be expected that the various maltose-containing syrups will assume stronger places as industrial commodities for use primarily as food ingredients. However, the commercial utilization of high maltose syrups is still limited at the present time due to the high cost of the enzymes used to prepare such syrups.
The production of the various maltose syrups from starch substrates generally involves a two step process. The first is the liquefaction of starch. In this step, the starch usually is suspended or dispersed in an aqueous medium and gelatinized by heat and then partially hydrolyzed using a thermostable alpha-amylase. The dry substance concentration of the starch suspensions or dispersions used in industry are usually about 30-40% and as a result the viscosity is extremely high after gelatinization. The temperatures necessary for jet cooking to obtain total gelatinization are usually about 105.degree.-110.degree. C. for most starch substrates. The preferred reaction conditions are usually a pH of about 6.0-6.5, a calcium ion concentration of 20-80 ppm, and a temperature of 90.degree.-100.degree. C. The hydrolytic reaction is terminated when the DE is about 5-10. Liquefaction also can be carried out by acidifying a starch slurry to a pH of 1.5-2.0 followed by heating at 140.degree.-150.degree. C. for 5-10 minutes.
The second step in the preparation of syrups from starch substrates is saccharification. Saccharification is the hydrolysis of oligosaccharides or dextrins to low molecular weight sugars such as glucose, maltose or mixture of these or their by-products. This is commercially done by a maltose producing enzyme such as a plant or microbial beta-amylase or fungal alpha-amylase. The saccharification is usually carried out at a pH of about 5.0-5.5 and at lower temperatures of about 50.degree.-55.degree. C. The lower temperatures are required because the commercially available saccharifying enzymes are heat labile. Furthermore, the action beta-amylases or fungal alpha-amylases is limited; they cannot act on alpha (1-6) linkages. Therefore, in order to produce extremely high maltose syrups it is necessary to also employ debranching enzymes such as isoamylase or pullulanase, which act on the alpha linkages, in addition to the beta-amylase or the fungal alpha-amylase. The high conversion syrups also are produced by saccharifying a liquefied starch at the lower temperatures and using both a beta-amylase or a fungal alpha-amylase and a glucoamylase. The use of the lower temperatures during saccharification present handling problems because of the higher viscosities and yield problems because of the formation of retrograde products.
There is a need for a method employing saccharifying enzymes at higher temperatures than those normally employed so that the problems associated with the low temperatures can be avoided.